Glow plug ignition systems or the like



June 24, 1958 D. ca. CARLSON 2,840,067

GLOW PLUG IGNITION SYSTEMS OR THE; LIKE Filed Sept. 23, 1954 2Sheets-Sheet 1 0 l5 gm CONTROL DEVICE Ec 2O DAVID G. CARLSON INVENTOR.

HIS ATTORNEY June 24, 1958 D. a. CARLSON 2,340,067

GLOW PLUG IGNITION SYSTEMS OR THE LIKE Filed Sept. 23, 1954 2Sheets-Sheet-2 FIG.3

DAVID G. CARLSON IN V EN TOR.

ms ATTORNEY United States Patent 2,840,067. GLOW PLUG IGNITION SYSTEMSOR THE LIKE David G. Carlson, San Fernando, Califi, assignor to HoffmanElectronics Corporation, a corporation of California ApplicationSeptember 23, 1954, Serial No. 457,878 6 Claims. 01. 123-145 Thisinvention is related to glow plug ignition systems for gasoline engines,or other internal combustion engines, and more particularly to animproved glow plug ignition system which is temperature controlled, sothat optimum operation may be facilitated. r

In the past, there have been many types of glow plug ignition systems.Such systems currently in use have been proven somewhat unsatisfactoryin that in starting an internal combustion engine associated therewith,glow plug burnout may occur as a result of large and varied currentsurges through the glow plug system. In addition, it is highlydesirable, for optimum operation, that the glow plugs maintain aconstant temperature throughout the entire period of running thecombustion engine.

Therefore, it is an object of this invention to provide an improved glowplug ignition system.

It is a further object of this invention to provide an improved glowplug ignition system which will exhibit glow plug temperature controlduring the starting and throughout the running cycle of an associatedinternal combustion engine.

According to this invention, an input voltage, for example one derivedfrom a generator associated with the engine incorporating the glow plug,drives a control device, e. g., magnetic amplifier, sensitive relay, orthe like, which is coupled to the input terminals of a Wheatstone bridgecircuit consisting of three impedance legs and a grow plug leg. Theoutput from the Wh-eatstone bridge circuit is fed back into the inputside of the aforementioned control device in such manner that,independent of the presence and magnitude of variations in the inputsignal driving the control device, the current through the glow plugs iscontrolled so that the operating temperature of the glow plug willremain substantially constant.

, The features of the present invention which are believed to be novelare set forth with particularity in the appended claims. The presentinvention, both as to its organization and manner of operation, togetherwith further objects and advantages thereof, may best be understood byreference to the following description, taken in connection with theaccompanying drawing, in which:

Figure l is a schematic diagram, partially in block form, of a glow plugignition system according to the present invention. f

Figures 2 and 3 illustrate particular devices which may be employed asthe control device incorporated in the circuit of Figure 1.

In Figure 1 an input'voltage is applied to input terminals and 11 ofcontrol device 12. Output terminals 13 and 14 of control device 12 arecoupled together through a first branch consisting of resistors 15 and16,

and a second branch consisting of a resistor 17 and glow,

plug 18. As is apparent, resistors 15, 16, 17 and glow plug 18constitute a Wheatstone bridge circuit. Junction 19, of resistors 15 and16, and junction 20, of resistors 17 and glow plug 18, are coupled tofeed-back terminals 21 and 22, respectively, of control device 12.

The circuit shown in Figure 1 operates as follows: Input signal E tocontrol device 12 is translated through control device 12 to appear asoutput signal E which is impressed across the Wheatstone bridge circuit,consisting of resistors 15, 16, 17 and glow plug 18. We shall assumethat, in the first instance, the value of E, is such that the currentthrough glow plug 18, and hence the temperature of the heating elementin glow plug 18, is at its desired value. Now let us assume that inputvoltage E and hence output voltage E increases positively. This meansthat since there is an increased voltage across terminals 13 and 14 ofcontrol device 12, the current through glow plug 18 will be increased.Hence, glow plug 18 will experience a temperature rise and a consequentincrease in internal resistance. between resistor 17 and glow plug 18will change, and consequently, a voltage will appear between junctionterminals 19 and 20, which we shall designate as E Voltage E issimultaneously applied to feed-back terminals 21 and 22 of controldevice 12 which, by virtue of the internal design of control device 12,will'reduce voltage E to compensate for the change in input voltage E,.This reduced output voltage E will reduce the current flow through thelegs of the Wheatstone bridge, and accordingly will reduce the current,and hence the temperature and effective resistance of glow plug 18.Thus, the resistance of glow plug 18 will be returned to its initial anddesired value. As indicated earlier, control device 12 may be a magneticamplifier in an A. C. system, or a relay in a D. C. system which reducesthe voltage applied to the Wheatst-one bridge, and hence to glow plug18, as the resistance of glow plug 18 rises. This is illustrated inFigures 2 and 3. In Figure 2, control device 12 includes a voltagedivider 200 coupled across input terminals 10 and 11 and having taps 201and 202 coupled respectively to contacts 203 and 204 of single-poledouble throw relay 205. Relay 205 is also provided with arm 206 coupledto output terminal 13 and also relay winding 207 coupled across feedbackterminals 21 and 22.

The operation of the apparatus of Figure l employing the apparatus ofFigure 2 is as follows. A feedback voltage derived from the bridge ofFigure l energizes relay 205 so as to impress a lesser voltage acrossoutput terminals 13 and 14 by virtue of the relay switching in a lowervoltage divider tap, i. e. tap 202. This condition is preserved untilthe bridge is restored to balance.

In Figure 3, magnetic amplifier 300 is provided with core 301, an inputwinding 302 coupled across input terminals 10 and 11, an output winding303 coupled across output terminals 13 and 14, and an appropriatelywound control winding 304 coupled across feedback terminals 21 and 22.

The circuit of Figure 1 employing the device of Figure 3 operates asfollows. In the presence of excessive input voltage, the feedbackvoltage developed by the bridge of Figure 1 is fed to the controlwinding 304 of magnetic amplifier 300 so as to reduce core flux andhence the magnetic coupling of the input winding 302 to the outputwinding 303, thereby reducing the voltage across the bridge and henceacross glow plug 18. Such voltage reduction' will lower the temperatureand hence the resistance of a glow plug 18 so as to restore the bridgeto balance. This technique has proven very effective in guarding glowplug ignition systems against starting current surges.

Accordingly, this invention devises a means whereby, regardless of themagnitude of the input signal and fluctuations thereof, the resistance,and hence the temperature, of glow plug 18 will remain substantiallyconstant. Experiment has confirmed the foregoing analysis, and thedesirability of the subject invention.

Thus, the ratio of resistance 2 3 While particular embodiments of thepresent invention have been shown and described, it will be obvious tothose skilled in the art that changes and modifications may be madewithout departing from this invention in its broader output terminals,and output circuit coupled to said output terminals, and first andsecond feedback terminals; first and second impedances coupled togetherin series between said first and second output terminals; a thirdimpedance and a glow plug also coupled together in series between saidfirst and second output terminals; the junction of said first and secondimpedances and the junction.

of said third impedance and said glow plug being coupled respectively tosaid first and second feedback terminals of said control device; saidcontrol device also including means coupled to said feedback terminalsand responsive to voltages therefrom for varying the coupling between 3said input circuit and said output circuit of said control device. I

2. Apparatus according to claim 1 in which said control device comprisesa magnetic amplifier.

3. An apparatus according to claim 1 in which said input circuitcomprises a voltage divider having first and second taps; said meanscomprises a relay having a relay winding coupled'to said feedbackterminals, first and second relay contacts coupled tosaid tapsrespectively, and a relay arm coupled to said first'output terminal toconstitute at least in part said output circuit;

4. Apparatus according to claim 1 in which said first, second and thirdimpedances include resistors.

5. Apparatus according to claim 2 in which said first, second and thirdimpedances include resistors.

6. Apparatus according to claim 3 in which said first,

second and third impedances include resistors.

References Cited in the file of this patent UNITED STATES PATENTS

